Origin and Habitat: Pfeiffera monacantha is distributed in Salta, northwestern Argentina, and in Cochabamba, Santa Cruz and Tarija, southeastern Bolivia. This is a wide-ranging species. It is frequent in suitable habitat, but the populations are not very large and are scattered.Type locality: Argentina, Salta, San Andrés (west of San Ramón de la Nueva).Altitude range: This species grows at elevations of 300 to 2,000 metres above sea level.Habitat and Ecology: This is an epiphytic or saxicolous cactus, that grows in seasonally dry east Andean valleys or Argentine yungas, mainly on cliffs. The main threat to this species is land use change due to cattle ranching.

Description:Pfeiffera monacantha is a slow growing and compact epiphytic shrub, freely branching. The spiny growth is both erect and triangular at first, later flat and pendent. This species produces minute waxy-orange blooms at every areole followed by small, round, waxy fruit that decorate the plant for months. Two subspecies are recognized, the nominate form and subsp. kimnachii (Doweld) Ralf Bauer.Derivation of specific name: The epithet monacanthum (Latin 'monacanthus,-a,-um'), “with one spine”, refers to the areoles often bearing only one spine.Stem: Branches flat to three-angled, and thin, linear-oblong, 2-3 cm broad, sometimes 45 cm long, obtuse, cuneate at base. Margin serrate. Apex acuminate or obtuse. Adventitious roots lacking.Areoles: White- or yellowish-felted and spiny, superficial, c. 12 mm apart, composite terminal areoles absent.Spines: 1 to 6, but usually only 1 or 2, stout, sharp, black, 5 to 10 mm long, also a few bristles.Flowers: Solitary at the areoles, borne laterally on upper segments near the shoot tips, waxy-orange, 1-1-5 cm long and to 2 cm in diameter. Pericarpels cup-shaped (± conical). Stamens numerous, c. 40-100, filaments and anthers white or whitish/cream. Pericarpel angled, sharply differentiated from perianth, tuberculate, with small scales, naked, but bristles and felt are occasionally developed. Hypanthium (receptacle tube) not developed.Fruit: Spherical more or less translucent, veiny, orange or pale pink, scaly.Seeds: Dark-brown to blackish, pitted, obovoid.

Subspecies, varieties, forms and cultivars of plants belonging to the Pfeiffera monacantha group

Cultivation and Propagation: Pfeiffera monacantha is among the easiest to cultivate epiphytic cacti and tolerates neglect. This cactus, being a native of the forests of Western Brazil, naturally requires different treatment from the desert cacti. It can grow up to 180 cm long when staked; it can also be grown in a hanging basket, which is more natural since it is an epiphyte. This cactus is green under ideal growing conditions but blushes red when stressed. Give it more heat or cold, less water or fewer nutrients, and you'll get that beautiful hue.Exposure: This plant prefers dappled shade.Watering: It requires ample water (more than other cacti) during spring and fall, but allow soil to dry slightly between waterings. Then stress the plant in winter and summer to encourage it to redden. Mist it occasionally, year-round, unless you live where humidity is high.Soil: These cacti won't want a normal cactus soil but will prefer to be in a soil largely composed of organic material, such as peat, sphagnum moss or leaf-soil, kept open by plenty of sharp sand or pumice grit. This type of soil would normally be used for orchids, bromeliads or other epiphytic plants. Regular potting soil is also fine as long as it drains well. PH, preferably about 5.5 to 6.0. Fertilization: It will want occasional doses of dilute fertilizer. Generally it is not suggested the use of manure for cacti, but in this case the addition of a quantity of old cow manure is beneficial and produces luxuriant growth. Hardiness:Pfeiffera monacantha is not frost-hardy and won't tolerate desert heat, but it thrives in coastal gardens. It needs night-time temperatures no cooler than 5° C, especially in the winter. In summer it need warm but not hot temperatures, preferably under 27° C. As it flowers during winter it should not be dried off like desert cacti but needs watering throughout the season. A resting period is not needed. Uses: Grow pfeiffera in a flat-backed pot against a light-coloured wall to show off the plant's striking colour and spider-like explosion of toothed leaves. Or use it as a cascading element of a potted composition with other succulents. These forest cacti tend to be long lived.Special requirements: These plants bloom profusely if grown in an even, high temperature, but significantly less if the temperature fluctuates between 4°C and 18°C. They drop their buds easily if they are moved. Once flower buds have formed, do not move the plant, as slight changes in environment may cause the buds to drop.Propagation: Stem cuttings. This plant can also be propagated from seed.